UNDERSTANDING MESH-BACKED COATING SYSTEM AND NON-SHIELDING

摘要

There has been much speculation and misinformation about the mesh-backed (geotextile) tape coatings and their non-shielding characteristics to CP. With all the discussions in the pipeline industry about cathodic protection (CP) shielding problems it is time to provide an understanding of just how a very good coating with sufficient dielectric strength can also be non-shielding to CP. The actual process by which this coating system proves to be non-shielding will be discussed. 'Non-shielding' in this context means if the coating system adhesion fails and water penetrates between the pipe and the coating, corrosion on the pipe is significantly reduced or eliminated because cathodic protection (CP) current is able to protect the pipeline in these disbonded areas. Therefore, a coating is shielding to CP if there is a disbondment, electrolyte is available between the coating and pipe and the CP current cannot reach the pipe under the disbondment, allowing corrosion to occur. After 25 years of service on thousands of jobs around the world, some mesh-backed tapes have record of being non-shielding to CP if disbondments occur.